Hydrogen sulphide

Hydrogen sulphide is a toxic and lethal gas produced in sewers and digesters under microbial anaerobic decomposition of organic matter.

Hydrogen sulphide (H2S) is a toxic and lethal gas produced in sewers and digesters under microbial anaerobic decomposition of organic matter. This organic matter is decomposed using oxygen that comes from the reduction of sulphate (SO42-). The resulting sulphide ion (S2-) reacts with hydrogen ions (H+) in the water and forms H2S.

H2S is a highly toxic and flammable gas. Hydrogen sulphide is heavier than air (density of atmospheric air 1.2 g/L, H2S 1.4 g/L) and thus tends to accumulate at the bottom of poorly ventilated spaces. H2S has a very characteristic odour and smells strongly like rotten eggs and flatulence.

It is detectable in low concentrations (ppm) and deadens the sense of smell in higher concentrations or after prolonged exposure. Respiratory paralysis and death may occur quickly at concentrations as low as 0.07% by volume in air.